1. Field of the Invention
The present invention relates generally to apparatuses and methods for communicating voice data in a wireless network, and more particularly, to providing voice services by a terminal in heterogeneous wireless networks.
2. Description of the Related Art
Wireless communication systems have been developed to provide communication services while users are on the move. Wireless communication systems started with voice communication services and can now offer high-speed data communication services.
For example, wireless communication systems for high-speed data communication services have been evolved from 3rd generation partnership project (3GPP) systems to long term evolution (LTE) systems. LTE systems may serve data communications up to 100 Mbps.
LTE systems have evolved to LTE-advanced (LTE-A) systems to speed up transmission. For ease of description, LTE system and LTE-A system are collectively referred to as LTE system, hereinafter.
Wireless local area networks (WLANs) come in use for covering a shadow area of a wireless communication service at low expenses. A WLAN is structured to expand the service area with access points (APs).
A wireless device selects an AP and links up with the selected AP in order to use communication services over a WLAN. For example, the wireless device can offer an AP selecting and linking schemes that are based on a basic service set (BSS) load over the WLAN.
In a wireless network where LTE networks and WLAN networks are mixed up, seamless handover between a WiFi network and a cellular network may be supported. In such a case, the serving base station may determine a handover to other base stations forming a heterogeneous network or homogeneous network.
The handover procedure between heterogeneous networks or base stations is typically performed by triggering the networks. However, handover between heterogeneous voice services may be done by triggering the terminal. By way of example, the terminal may determine whether to hand over between an LTE network-based voice service (Voice over LTE (VoLTE) service) and a WiFi network-based voice service (Voice over WiFi (VoWiFi) service) and trigger handover based on the determination. In such a case, the references by which the terminal determines whether to hand over may have a significant effect on handover performances. Accordingly, the references need to be prepared for enhancing the performance of a handover between heterogeneous voice services.